Electron discharge tube



Feb. 4, 1936.

H. ROOSENSTEIN ET AL vVLFECTRON DISCHARGE TUBE Filed June 28, 1954 INVENTORS WOLFGANG KAUTTER ORST ROTHE ATTORNEY HANS OTTO RDOSENSTEIN Patented Feb. 4, 1936 UNITEDl STATES 'l' OFFICE ELECTRON DISCHARGE TUBE tion of Germany Application June 28, 1934, Serial No. 732,774 In Germany July 5, 1933 1 Claim.

Our invention relates to electron discharge tubes havingv indirectly heated cathodes, more particularly to means for shielding the cathode heater leads from the electrodes mounted-within the tube.

In radio receiving sets and in ampliers, electron discharge tubes Yhaving indirectly heated cathodes are used extensively, the current supply for the cathode heater being thru transformers or resistances in series with the line. disturbances are often occasioned because of the fact that the alternating voltage for energizing the heater is capacitvely transferred to the other electrodes in the tube by way of the cathode heater current supply leads. In order to obviate these difliculties various attempts have been made to provide electrostatic shielding inside the tube between the heater leads and the electrode in the tube. However, experience has shown that, especially when the demands with respect to freedom from hum of the set are severe, or where ampliers designed for high gains are concerned, the plan of conning the shielding means to the interior of the discharge tube is not adequate, in fact, that it is necessary to extend the shielding means also to the outside of the tube.

It is an object of our invention to provide an electron discharge tube in which the cathode .heater leads and the leads to the other electrodes within the tube are electively shielded from each other both inside and outside ofthe tube.

According to our invention, we provide shielding which will satisfy even the severest requirements by positioning within the tube electrostatic shielding means connected to the cathode sleeve and extending transversely of the tube to thewall of the bulb or envelope, additional shielding means being provided exteriorly of the tube to adjoin the shielding within the tube. What is meant by an electrostatic union or connection in the present instance is that the external shielding means extends parallel to the shielding inside the tube for such a distance or in such close proximity thereto as to constitute a continuation of the shielding, so that disturbing or stray potentials acting on the heating current supply leads located on one side of the shield will be unable to set up an appreciable field upon the other side of the shield thru the interstitial space between the two shields. 'The shielding means mounted inside and outside the tube are suitably connected conductively with each other, while where this plan is diicult of practical adoption, or where this is not possible due to a difference of potential In operation,

(Cl. Z50-27.5)

connected, the coupling capacity being formed by the shields provided inside and outside the envelope of the tube. 'Ihe shielding means could be formed in part by a metallic deposit or coating upon the Wall of the bulb.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claim, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a schematic diagram of an electron discharge tube embodying our invention; Figure 2 is a longitudinal section of a modication of an electron discharge tube embodying our invention; Figures 3 and 4 are schematic longitudinal sections of modifications of electron discharge devices embodying our invention. Figure 5 is a schematic diagram of a modification of Figure 1.

Referring to Figure 1 the ceramic cathode support l has positioned within it the heater element 2, which is provided with supply leads 3 and 4. Surrounding the cathode support is a metal sleeve 5 closed at the top and having upon it the electron-emissive coating. Disposed around the cathode are the other electrodes, for example, the grid B and the plate 'l in the usual manner. The electrode assembly is mounted inside the glass bulb or envelope 8. United with the cathode sleeve or bushing 5 is a shield 9 which extends as far as the inner wall of the glass bulb 8, a continuation I0 being provided on the outside of the envelope in the form of a shielding case. The two shielding means 9 and Ill extend a certain distance parallel to each other so that all of the lines of force emanating from the heating current leads 3 and 4 will be conned within the shields, with the result that the space outside the shield will be practically free from any disturbing eld actions. Inside the shielding case l0 is suitably disposed the heating transformer Il. Connection with the supply line is established by way of a shielded cable I2. For the purpose of insuring perfect shielding it is advisable to establish a conductive connection between the shields 9 and I0 disposed inside and outside the tube, for example,

by means of conductor I3 as shown in Figure 5, and to connect both shields to ground. Wherever a conductive connection is impossible, for example, because of difference of potential, the connection can be secured by means of a condenser, the capacity of the latter being chosen so high that it constitutes practically a shortcircuit path for stray alternating currents.

In Figure 2 in so far as equivalent elements are concerned, the same reference numerals stand for similar parts as in Figure 1. The cathode sheath or sleeve is extended into and sealed in the press 20. In order to insure a vacuum tight seal for the cathode sleeve, a glass tube is placed over the metallic sleeve and the latter may then be fused in the press to provide the downwardly extending tubular portion 2l of glass. Over the glass portion 2| is a metal tube 22 which ex'- tends as far as the bottom of the tube base 23. The shielding is continuedat the mounting plate of the set which is coated with a metal foil 24. The socket contacts 25 and 26 are disposed inside the metal tube 2l which forms a continuation of the metal tube 22 in the base of the tube. The heating voltage is supplied by means of `a shielded cable 28.

In Figure 3 the heater leads are sealed in the glass envelope at the opposite end from the rest of the electrode leads. Connected with the 'cathode sleeve 5 is a metal shield 30 which extends transversely of the tube to the inside wall of the glass bulb and practically divides the interior of the bulb into two parts. The glass bulb is externally provided with a metallic coating or shield 3l which may extend only from the shield 3U to the bottom of the tube. The shield 30 has a rim parallel to the outer shield 3 l, forming a condenser of which the dielectric is the wall of the bulb. In this manner an electrostatic coupling is established between shield 3B and the outside shield 3|. A shield 32 is provided externally which adjoins the outside shield 3l of the tube and thus completely shields the heater supply leads from the other electrode leads.

In Figure 4 the tube is provided with two presses. Thru the upper press 49 are brought only the heater leads, whereas the lower press 4l contains all of the other electrode leads. The cathode sleeve 5 is extended into and sealed in the upper press 40. The press is surrounded by a metallic bushing or collar 42 which extends parallel to the extension of the cathode sleeve. In the same way as before, the shielding collar 42 connects with an outwardly extending shielding wall 43 which thru collar 42 is in close capacitive relationship with the cathode 5.

While we have indicated the preferred embodiment of our invention of which we are now aware and have also indicated only one specic application for which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claim.

We claim,-

An electron discharge tube having an envelope, an indirectly heated cathode positioned within said envelope and having a sleeve closed at one end, a heater extending within said sleeve and provided with leads extending thru one end of said envelope, concentric electrodes surrounding said cathode sleeve, leads from said cathode and said concentric electrode extending thru the opposite end of said envelope from said heater leads, a shield extending transverse' of the envelope into proximity of the envelope, and electrically connected to said cathode sleeve, a metallic coating on the outside of said envelope capacitively connected to said transverse shield and a transverse shield exterior of and adjacent the end oi" the envelope thru which the leads from said cathode and said concentric electrode extend and electrically connected to said outside metallic coating.

HANS OTTO ROOSENSTEIN. WOLFGANG KAUTTER, HORST ROTHE. 

